The invention relates to a driving hub for a vehicle and, in particular, a driving hub with a friction gear of which the gear ration can be smoothly adjusted.
U.S. Pat. No. 4,735,430 discloses a driving hub for a bicycle of which the hub sleeve rotatably mounted in the bicycle frame is driven via a friction gear arranged in the hub sleeve with a hub shaft which is set into rotation by the pedals. The friction gear comprises two toroidal discs which are rotatably mounted on the hub shaft and are joined together in terms of friction via several friction wheels. The friction wheels are rotatably mounted on spindles which, in turn, are pivotal on a stationary friction wheel carrier round pivot pins extending in the tangential direction of the toroidal discs. One of the two toroidal discs rests axially movably on the hub shaft and is pressed via an expanding clutch provided with oblique slide faces against the friction wheels as soon as the hub shaft is driven. The other toroidal disc is coupled via a planetary gear and an overrunning clutch to the hub sleeve. For smooth adjustment of the step-up ratio of the friction gear, the spindles of the friction wheels are extended radially outward and engage in oblique slide slots of a control sleeve which is arranged inside the hub sleeve and rotatably surrounds the friction gear. The oblique position of the friction wheels relative to the hub shaft and therefore the step-up ratio of the friction gear can be altered by turning the control sleeve by means of a traction cable arrangement.
In the known driving hub, the hub sleeve is radially guided via the control sleeve on a housing of the friction gear. The wheel load complicates adjustment of the step-up ratio. As both toroidal discs have to be movably guided with the known driving hub, not only do production problems arise but also the reliability of operation and service life are adversely affected. Finally, the known driving hub requires special assembly means as the hub shaft has to be rotatably mounted in the bicycle frame other than with conventional driving hubs. The axial fixing of the hub sleeve relative to these assembly means is not sufficient for many applications with the known driving hub. Finally, special designs of a control mechanism are required for controlling the step-up ratio.